A device for measuring air throughput in an intake tube of an internal combustion engine, which has a hot wire disposed in a bridge circuit, has been known. By regulating the electric current, this hot wire is held to a constant excess temperature relative to the temperature of the aspirated air, and a voltage which serves as the measurement signal may be picked up at one of the bridge resistors.
The independence of the measurement voltage from the temperature of the aspirated air is attained by having not only the hot wire but also a further resistor of the bridge circuit be dependent on temperature. When this measuring device is used during vehicle operation, soil particles are deposited on the hot wire. As a result, the known device provides that the hot wire be subjected from time to time to a high current in order to burn off these deposits. This burn-off procedure is realized via a specific bridge imbalance, which thus causes an increased flow of electric current through the hot wire.
In the known device, this is effected by switching a further resistor parallel to one of the bridge resistors upon the occurrence of a trigger signal. As a result, the regulating amplifier causes the hot wire to assume a higher excess temperature relative to the aspirated-air temperature.
However, it is found by the present invention to attain an optimal burn-off of the hot wire, the specific wire temperature must be adjusted as precisely as possible. If the burn-off temperature is dependent on the aspirated-air temperature, as is the case in the known devices, then the wire will not be sufficiently well cleaned when the ambient temperature is low; alternatively, if the ambient air temperature is high, the hot wire might be damaged.